Deal with withdrawn metadata

[srappel]

As institutions may remove items from OpenGeoMetadata, they will not necessarily be removed when we update our repositories and re-index. That's because records are only updated if a new record is ingested that matches the id.

Would it make sense to run a rake task to delete the whole index periodically to catch these? Is it that sample? Is there a downside to this? How often would it need to happen? Is there some better way?