docs: def _reset_server(self, address):
          """Clear our pool for a server and mark it Unknown.
  
          Hold the lock when calling this. Does *not* request an immediate check.
          """
          server = self._servers.get(address)
  
          # "server" is None if another thread removed it from the topology.
          if server:
              server.reset()
  
              # Mark this server Unknown.
              self._description = self._description.reset_server(address)
              self._update_servers()