The WebProcess has a cached-in-memory copy of everything for site A, and the UIProcess has its own cached-in-memory copy for site A. But as the WebProcess and the UIProcess start changing items, they'll just get further and further out of sync. -WebProcess will only see the items that existed when it first read them in, plus whatever changes the WebProcess has made. -UIProcess will only see the items that existed when it first read them in, plus whatever changes the UIProcess has made. -On disk, the "most recent changes commited to disk" will win out. <rdar://problem/9383302>