Control systems and methods for cache coherency are provided. One control method includes steps of transmitting a link-connect request to a second electrical device when the first electrical device is coupled to the second electrical device by a cache coherency (CC) interface by a first electrical device, establishing a link between the first electrical device and second electrical device according to the link-connect request by the CC interface, and operating a first operating system of the first electrical device by a second processing unit of the second electrical device after establishing the link.