The MIC processor is used as a coprocessor, similarly to a GPGPU. It is effectively the Larrabee architecture: "Design elements inherited from the Larrabee project include x86 ISA, 512-bit SIMD units, coherent L2 cache, and ultra-wide ring bus connecting processors and memory."

The hardware maintains cache coherency across the cores, and presents a programming model that is the same as a multi-core Xeon. Except, the cores are in-order, and have 512 bit vector units attached, and the communication times for cache misses are quite different.

More at: Architecture overview MIC wikipedia