Browser technology makes tracking goals on cross domains a little tricky for every “client side” platform and some custom integration is necessary.
The only goal type that can be measured on cross domains, is the “custom” one.
Lets say you have two totally different domains – domain-one.com and domain-two.com and you want to set an experiment on domain-one.com which sends the visitors to domain-two.com and you want to track how many of them convert on domain-two.com.
Well in order to do that, on the domain-two.com page, on which you want to track conversions ( like domain-two.com/thank-you.html ) , you must insert an iframe, in the body of the thank you page, that contains a link to a custom page (conversion.html) hosted on the original domain/website which in this case is domain-one.com.
The iframe script that must be inserted is the following:
<iframe src="http://domain-one.com/conversion.html" style="display:none;"></iframe>
The conversion.html page is a stand alone html page, hosted on the domain-one.com that should contain the following code:
You can load this iframe with a GET parameter, so that you can send the proper goal value.