How does the current Notification Service handle stale registrations that have been marked as stale?

Question

I was hoping to simply send silent push notification to a tag and have Notification Server "mark the stale registrations" and then later (at its convenience?) delete these from its database, so that we can keep our quota. However so far I have not seen any evidence that these registrations are being cleaned up, even for cases where real push notifications have been sent to the tags. I know there are approaches we can take to proactively clean up, but based on what I have read it seems that Notification Hub will take it upon itself to mark stale registrations when they are identified by tag pushes and then delete these during some sort of maintenance cycle. Does anyone know what the real answer is. I prefer to have Microsoft clean these out rather than doing this ourselves.