Network Hook Information

In the new 3.0 version, when the Network is enabled, is there a filter hook that limits the posts displayed in the loop to only those that belong to that site? If there is such a filter, I would like to write a plugin that will unhook this filter so that I can display all of the posts from all of the sub-sites on the main site page. For example, post on subsite.rootsite.tld gets displayed in rootsite.tld ‘s loop.