Country Detection for URL redirect (Shopping Cart)

Question

I want have two domain names
www.demo.com.au
www.demo.co.nz
If a viewer from New Zealand (NZ) visits the Australian site (.com.au), I want the website to detect that they are from New Zealand and redirect them to the NZ domain. 
I found this Javascript code on the Business Catalyst KB, however it seems to loop over and over again, even though there are breaks included in the script.
<script language="javascript">
var country = '{module_visitorcountrycode}'; // e.g. var country = US;
switch (country) {
case 'US':
document.location = 'http://us.yourcompany.com';
break;
default:
document.location = 'http://www.yourcompany.com';
break;
</script>
I've read that I should use cookies but I'm not sure how to implement that with the above script.
Any help would be much appreciated. 
Kind Regards
Brendon

Answer 1

Thanks Liam.  Maybe something more along these lines then"?
<script language="javascript">
var country = '{module_visitorcountrycode}'; // e.g. var country = NZ;
var countryCookie = document.getcookie(countrycode);
if countryCookie == 'NZ';
switch (country) {
case 'NZ':
document.location = 'http://www.google.com';http://www.demosite.com.au'; // current page;
break;
default:
document.location = 'http://www.demosite.co.nz'; // page to be redirected to;
break;
</script>