Well, sometimes it's better to look first and blog second,
I looked around a bit and found that the CRM Team Blog actually have an entry on how this works. Have a look here: https://blogs.msdn.com/crm/archive/2006/08/15/701230.aspx
The SubscriptionSyncInfo table seems to be the place where all syncs are logged to the database. Very usefull for checking if a users sync has been successfull and how often it has been done.
CRM and SharePoint Consultant