Multi-vehicle systems composed of Autonomous Guided Vehicles (AGVs) are largely used for industrial transportation in manufacturing and logistics systems. Deployment of a team of AGVs raises management and coordination problems such as deadlock and collision avoidance, conflict resolution, and shared resources negotiation. Decentralized approaches are more suitable than centralized ones for dealing with coordination problems due to the gains in terms of scalability. In a decentralized approach reliable dissemination of AGV state is a crucial operation that is however often neglected. The present paper proposes an efficient reliable protocol for multi-vehicle systems state information exchange among neighbours. This "Neighbourhood Monitoring" protocol allows for developing a reliable decentralized coordination scheme which is suitable for systems with large number of vehicles. The performance of the protocol is evaluated from several standpoints.