In this paper, we present the 'Co-Forgetting Protocol' as a robust and efficient mechanism for shared knowledge management of multi-agent systems (MAS) in complex and dynamic environments. The protocol integrates three core components: (1) context-aware semantic voting using the lightweight DistilBERT model, (2) multi-timescale decay functions, and (3) a PBFT-based consensus mechanism to enable synchronized memory pruning in MAS. Experimental results show that it reduces the memory space by 52%, achieves 88% voting accuracy, 92% PBFT consensus success rate, and 82% cache hit rate in a simulation environment with four agents. gRPC, Pinecone, and SQLite are utilized to ensure efficiency and scalability of inter-agent communication and data management.