Efficient CMP utilisation requires virtualisation. This forces multiple applications to contend for the same network resources and memory bandwidth. In this paper we study the cause and effect of network congestion with respect to traffic local to the applications, and traffic caused by memory access. This reveals that applications close to the memory controller suffer because of congestion caused by memory controller traffic from other applications. We present a simple mechanism to reduce head-of-line blocking in the switches, which efficiently reduces network congestion, increases network performance, and evens out the performance differences between the CMP applications.