Periodically websites carry news of blog networks being deindexed
overwhelmingtraffic.com/backlinks/google-finds-and-destroys-blog-networks/
Most huge networks with thousands of domains are highly automated and leave footprints which can be easily detected, and most online activities are closely monitored.
If you have hundreds of domains deindexed, one way to deal with this is to recycle content and blogs, web hosting accounts can always be configured as required.