As with the login screen, the logout screen is provided centrally by SSO.

You just need to construct a URL like this for logging out a user:

https://websignon.warwick.ac.uk/origin/logout?target=http%3A%2F%2Fblogs.warwick.ac.uk%2Fkieranshaw%2F

As you can see, this is just the SSO logout url with the return target URL encoded in the target parameter. SSO will deal with destroying the WarwickSSO cookie and invalidating the users session. When the user returns to your application, the cookie will be gone and the user logged out centrally.