code: def mark_as_forwarded(self, req: Request, to: int):
          
          self[req.key].forwarded = True
          self[req.key].forwardedTo = to
          self[req.key].unordered_by_replicas_num = to
docs: Works together with 'mark_as_executed' and 'free' methods.
  
          It marks request as forwarded to 'to' replicas.
          To let request be removed, it should be marked as executed and each of
          'to' replicas should call 'free'.