I don't use Windows for anything since I got the Notes client running on Unix (and it is faster than on Windows, too), so I don't know what Windows domains are, however, midrange and high-end Solaris servers are partionable and can multiple domains. A domain in these servers are hard partionalbe and have a certain number of cpu's and memory plus other resources allocated to them.
With Solaris 10 you can use zones that can be thought of as soft partitions. But you cannot run multiple OS versions. With partitions each domain can have its own OS version.
Don't know if that helps.