Will Membership cross domains when used with user syncronization?

I had a great meeting with a marketing team and a gentleman building a nation group.
I should say groups.

They want to start with a yellow page site and connect it to the main site later. I know the user synchronization wil sync the users. Will the membership plug in cross domains as well?
Also, if they build the groups in a third domain will it be able to be controlled by the member plugin as well?
Thanks for your time.
Proud to be a WPMU Dev member