Implementing Single Logout
Sun identity architect Pat Patterson and I just cowrote Single Logout: A Demo, a sequel to a February article on Project Lightbulb (OpenSSO's SAML 2.0 PHP Extension). Besides updating you on how Project Lightbulb has evolved, the sequel describes how to terminate user sessions with all the members in a Circle of Trust through Security Assertion Markup Language (SAML) 2.0 PHP.
In particular, take a look at the code segments that illustrate the process. I learned a lot in cowriting the article with Pat and thoroughly enjoyed the experience.