Open Core Protocol (OCP) is a common standard for Intellectual Property (IP)core interfaces. OCP facilitates IP core plug-and-play and simplifies reuse by decoupling the cores from the on-chip interconnection network and from one another. Enabling hardware cache coherence support at OCP cores requires the OCP interface to generate and receive additional coherence messages in order to invalidate cache lines cached at the core side or transfer cache lines and their ownerships between OCP cores. In this article the concept of OCP coherence extensions is proposed. Moreover, a possible OCP-based coherence design utilizing the proposed OCP coherence extensions to support system-level cache coherence is also demonstrated.