Help:Purge
To manually clear the webpage cache, just point your browser to:
http://yoursite.tld/index.php/Main_Page?action=purge
Notice the "?action=purge" portion of the URL.
For those of you that must use "Ugly Links", you'll need this syntax:
http://yoursite.tld/index.php/index.php?Main_Page&action=purge
The important part for these people is to use an ampersand instead of a question mark when adding the purge command: "&action=purge".
For either method, please note that you will need to change the "yoursite.tld" to match that of your actual Wiki.
If you purge a page this way without being logged into the wiki, a confirmation form will come up asking you to confirm that you want to purge the page. This is a precaution to keep web spiders from purging pages accidentally when following links.