Everyone gets KB now, the old core vs active knowledge licensing no longer exists. Can you spell out what you mean by ' added a security group to each of the domains'?
A common issue when you have knowledge domains/partitioning is that you need to be searching as someone who is in a group that has been given access to the knowledge domain containing the articles in question. I used to login as SA expecting to see every knowledge results search coming back, but that doesn't happen unless SA is a member of at least some groups that have been given knowledge domain access.
You could also turn on the TPS diagnostics to see what is happening when you fire off a search.
You could also take a look through the enclosed.