...
During normal logout in Sakai, only the Sakai sessions are session information is cleared. To ensure that the DistAuth cookies are deleted also, one must modify the LoginTool.java file in the sakai-2-0-1-src\login\login\src\java\org\sakaiproject\tool\login directory. An additional parameter can be added to the sakai.properties file so that the logout url is correctly referenced.
Steps involved, for Sakai 2.0.x
#1. modify the complete() method to be the following:
...