[Mediawiki-l] Where are user options cached?

[Daniel Barrett]

After changing the default skin on our wiki from monobook to vector ($wgDefaultSkin = 'vector'), and deleting all 'skin' preference rows from the user_options table, a few of our wiki users still see the old skin, monobook. Where is this setting cached?

Things that did not help (monobook still shows):

*       Logging out and logging back into the wiki
*       Hard-refreshing the browser (ctrl-F5)
*       ?action=purge
*       Using a different browser (e.g., Chrome instead of Firefox)

What worked:

*       Visiting Special:Preferences and simply clicking Save.

So this caching, whatever it is, happens at the user account level, not the browser level. Where does it exist and how do you clear it?

Thanks for any info,
DanB