How do you programmatically change an image in DataGrid cell

Question

I have a DataGrid which contains a status icon. I have been able to get the initial status icon to show in the DataGrid. But I am unable to update the it. I basically need to update the image for a selected row with either a 'assets/processing.png',  'assets/success.png' or 'assets/failure.png' image. I just cannot seem to be able to figure out how to get access to the image in the necessary cell to update/replace it. I've tried to make it a property of my ArrayCollection data provider, but that does not work. I've also have tried to some how get a reference to the original image so it can be replaced, but cannot figure out how to do such. Below is the code to my DataGrid. I will be very appreciative of any help on this. (I'm relatively new to Flex/ActionScript, but a seasoned developer otherwise.)
<mx:DataGrid id="myDataGrid" left="0" top="0" bottom="0" right="0"
                     allowMultipleSelection="true" verticalScrollPolicy="on"
                     draggableColumns="false" resizableColumns="false" sortableColumns="false"
                     dataProvider="{myArrayCollection}">
            <mx:columns>
                <mx:DataGridColumn headerText="Name" dataField="name" wordWrap="true" />
                <mx:DataGridColumn headerText="Status" dataField="status" width="75" textAlign="center">
                    <mx:itemRenderer>
                        <mx:Component id="statusComponent">
                            <mx:HBox id="imageBox" width="100%" height="100%" horizontalAlign="center">
                                <mx:Image id="statusImage" source="@Embed('assets/pending.png')" width="16" height="16"  />
                            </mx:HBox>
                        </mx:Component>
                    </mx:itemRenderer>
                </mx:DataGridColumn>
            </mx:columns>
        </mx:DataGrid>

Answer 1

Mark,
My sincerest thanks for your assistance. myDataGrid.invalidateList() the key thing I was missing in all my previous attempts. I had thought about  needing to do something to refresh the grid, but was looking for a "refresh" method. I did not see the invalidateList() method.
To get it to work I needed to override the Container's set data method within the status image column (see below for my full example). Without this, it does not work. Am I missing something or is there a better way to do this?
Again, thank you very much for your help.
<?xml version="1.0" ?>
<mx:Panel xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="init()">
  <mx:Canvas width="100%" height="100%">
    <mx:DataGrid id="myDataGrid" left="0" top="0" bottom="0" right="0"
                 allowMultipleSelection="true" verticalScrollPolicy="on"
                 draggableColumns="false" resizableColumns="false" sortableColumns="false"
                 dataProvider="{myArrayCollection}">
      <mx:columns>
        <mx:DataGridColumn headerText="Name" dataField="name" wordWrap="true" />
        <mx:DataGridColumn headerText="Status" dataField="status" width="75" textAlign="center">
          <mx:itemRenderer>
            <mx:Component>
              <mx:HBox width="100%" height="100%" horizontalAlign="center">
                <mx:Image id="statusImage" width="16" height="16" />
                <mx:Script>
                  <![CDATA[
                  override public function set data(value:Object):void
                    if (value != null)
                      statusImage.source = value.status;
                  ]]>
                </mx:Script>
              </mx:HBox>
            </mx:Component>
          </mx:itemRenderer>
        </mx:DataGridColumn>
      </mx:columns>
    </mx:DataGrid>
  </mx:Canvas>
  <mx:Button id="updateButton" click="updateIcon()" label="Update Icon" />
  <mx:Script>
  <![CDATA[
    import mx.collections.ArrayCollection;
    [Embed(source="assets/success.png")]
    public static const successImage:Class;
    [Embed(source="assets/fail.png")]
    public static const failImage:Class;
    [Embed(source="assets/pending.png")]
    public static const pendingImage:Class;
    [Bindable]
    private var myArrayCollection:ArrayCollection = new ArrayCollection();
    private var lastIndex:Number = 0;
    private function updateIcon():void
      //sample updating
      var item:Object = myArrayCollection.getItemAt(lastIndex);
      (lastIndex % 2 == 0) ? item.status = EmbeddedImages.successImage : item.status = EmbeddedImages.fail1Image;
      myDataGrid.invalidateList();
      if (++lastIndex > myArrayCollection.length - 1)
        lastIndex = 0;
    private function init():void
      //load some dummy sample data for demo/testing
      for (var i:Number = 1; i <= 10; i++)
        myArrayCollection.addItem({
          name:"value-" + i,
          status:pendingImage
    ]]>
    </mx:Script>
</mx:Panel>