Unfortunately, Single Logout from Shibbolized applications such as EdSpace (Confluence) and MCNC's public website will work reliably only in some cases. Therefore, the recommended way to log out is to QUIT OUT OF YOUR WEB BROWSER. It's the quickest, most reliable way plus it also logs you off from other sites you previously logged into such sites as PayPal, etc.
An alternate (though less recommended) way is to manually delete all of your browser's session cookies.
If you're interested in more details, please see this presentation for some more useful details: