This will avoid careless forkers polluting the shared database
even if they make their own chain. They'll then automatically
start using another subdb, and any key-reusing fork of those
forks will reuse their subdbs.
It scans for known spent outputs and stores their public keys
in a database which can then be read by the wallet, which can
then avoid using those as fake outs in new transactions.
Usage: monero-blockchain-blackball db1 db2...
This uses the shared database in ~/.shared-ringdb
