Setting up TS Session Broker in Server 2008 R@

Hi Experts.  I see from the prerequistes of deploying TS Session Broker to a Terminal Server Farm that the server has to be part of a domain!!    I cant see anywhere references to the rest of Terminal Server Farm.  Does that mean that all TS Servers must be part of the same domain?    Or can they be standalone.    Does is also mean that the users that need to log onto the Terminal Server Farm have to be part of the same domain as the TS Session Broker? Can they be part of other domains, or even workgroups?   Doesnt seem to be a lot of information on this.   Thansk for any help.