I found myself in serious need to have Google Calender Sync (GCS) to forget about sync-ing deleted Outlook Calendar items. If GCS does not forget, it would then delete the same items on Google Calendar, too! And that's very bad for me!
Luckily, after some hack, I found one way: just delete saved state files of GCS. It works like this:
- Exit GCS.
- Go to the folder named:"%USERPROFILE%\Local Settings\Application Data\Google\Google Calendar Sync\data_files"
- Removing all files, except "user_properties.txt" and "user_info_2.txt".
- Restart GCS. It is done!
Reference: Sync with Microsoft Outlook™ calendarNew!