[wp-forums] Need help with rewrite rules flushing

[ipstenu at ipstenu.org]

Short version - Some people (very very few that I've seen in my  
non-scientific check, but a more-than-zero number) reported that they  
got 404s after upgrading. Resetting permalinks fixes this.  Problem is  
what about MultiSite?  These folks have hundreds of sites.  Is there a  
way to do this?

http://wordpress.org/support/topic/404-errors-after-update-need-to-flush-rewrite-rules-network-wide