Message-passing mechanism is commonly used to preserve data coherency in distributed systems. This paper presents an algorithm for insertion of minimal message-passing in system-level design to guarantee data coherency. The target architecture is a multi-component heterogeneous system, where some components have local memory (or they are memory components by themselves. The algorithm enables automatic insertion of message-passing during system-level design to relieve designers from tedious and error-prone manual work. The optimal solution given by the algorithm also ensures the quality of automatic insertion. Experiments show that the automatic approach achieves a productivity gain of 200X over manual refinement.