I don't think you can forcefully end another users session.
You probably have to flag/signal the termination in some application scoped component and then have the client poll that place and have the client self-destruct...
Maybe you can write some example?
Dont be lazy ;-)
* Write an application scoped bean with a Set that contains something identifying the user (session, user id etc).
*Add a method that queues the id for destruction.
*Add a boolean method that checks if the set contains() id.
*Add a page action that uses the boolean method and logs out if it returns true.
As I said, there might be better ways.
Of course polling against JMS or some sort of push (depending on view technology) might be cleaner.