I assume you mean the http session. Just never save anything to
http://docs.grails.org/latest/ref/Servlet%20API/session.html the session. You are probably most likely wanting to be Restful and Stateless (which is good).
This is what you are aiming for
"Statelessness means that every HTTP request happens in complete
isolation. When the client makes an HTTP request, it includes all
information necessary for the server to fulfill that request. The server
never relies on information from previous requests. If that information
was important, the client would have sent it again in this request"
Read up on REST, Restful architecture, Grails supports it very well.