main homepage not updated automatically

[nickdine]

Hi, I have a network wordpress setup with WordPress MU Domain Mapping and sitewide tag so that when I create a post in one of the subblog, a copy of that post will appear in the main blog.

Under the Dynamic Cache setting I have Single + Front Page.
The problem is that whenever I create or edit a post in sub blog only that post's cache will update, how can I setup so that the Main blog's homepage will also gets updated?