Macbook Pro, how to reset invalid external display resolution?

Hi there. I have a question about the external display configuration.
I recently connected my 2011 Macbook Pro 13" (10.8.2 Mountain Lion) to an external HD-TV using Thunderbolt to VGA adapter. After connecting the TV had 1920x1200 resolution which made the text and everything look very tiny. So I thought I'd lower the resolution a bit. But then I messed up and accidentally changed the resolution and refresh rate for the external display to one that wasn't supported. So the TV went black and gave an error about an invalid resolution. At the same time, on my Macbook screen I had only the background image and display settings dialog. No mouse cursor, no menu bar, no dock etc. So I couldn't do anything.
I disconnected the Thunderbolt adapter and got my Macbook screen back to normal, but when I plugged it in again, the same thing happened. Invalid resolution on TV, just background image and display settings on Macbook screen.
Now, this was just before I was going to give a presentation and it resulted in a very awkward situation with me franticly re-plugging the Thunderbolt adapter and looking just completely clueless In the end I had to borrow my colleague's laptop.
So my question is: when this happens, is there a way I can reset / clear the external display settings back to defaults? They are obviously saved somewhere since replugging the Thunderbolt adapter didn't give me back my original resolution.

A PRAM reset should solve that:
From the article linked above:
Your Mac stores certain settings in a special memory area even if it is turned off.  On Intel-based Macs, this is stored in memory known as NVRAM; on PowerPC-based Macs, this is stored in memory known as PRAM.
Information stored in NVRAM / PRAM includes:
Speaker volume
Screen resolution
Startup disk selection
Recent kernel panic information, if any
To reset your PRAM:
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.

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