1. A method for managing user sessions within a distributed data processing system, the method comprising: in response to determining to logoff a user on a system within a first domain, obtaining a list of domains at which the first domain has initiated a logon operation for the user by providing an authentication assertion; generating at a system in the first domain a logoff request message for the user for each domain in the list of domains, wherein a logoff request message comprises an authentication assertion for the user; and sending a logoff request message to each domain in the list of domains.