In previous version of OS X, the iSync application could be used to reset sync history. This technique often resolved a bunch of miscellaneous bugs and sync-related problems. The iSync application has since been removed in OS X Lion and Apple's support documents aren't of much help. This one claims that resetting sync services can be performed from iSync in Leopard and from the Sync menu extra in later version of OS X. This document describes how to enable the menu extra in the MobileMe settings. Besides the fact that MobileMe is deprecate and no longer in use, the option described in that document to enable the Sync menu extra only appears after signing in to MobileMe... Which is deprecated.

Fortunately, there's a hidden folder you can open to enable any menu extra manually! Open Finder and select Go > Go to Folder (or press Command+Shift+G). In the prompt that appears, type: /System/Library/CoreServices/Menu Extras/. This should bring you to a folder with a bunch of menu extras that you can double-click to add to the menu bar. The one of interest in this case is Sync.menu, which should appear in your menu bar a second or two after opening it.

Once it's in your menu bar, hold Alt/Option and click on it to expose the advanced options and click "Reset Sync Services". After that's done, you can remove it from your menu bar if you'd like by holding Command and then clicking & dragging it out from the menu bar.