Consider using profiles to define different site domains and login credentials (if needed). From there, you can put your test case in a Test Suite, then put duplicates of that Suite into a Test Suite Collection each Suite can then be executed using each of the profiles you have defined. This should allow you to reuse the same test case and object references across multiple domains assuming they share similar source code.
Additionally, here’s a helpful link demonstrating looping over multiple objects within a Test Case.