1. A computer-implemented method for detecting errors in a computer system comprising a plurality of clusters, each cluster including a plurality of local nodes and an interconnection controller interconnected by point-to-point intra-cluster links, communications between the local nodes and the interconnection controller made via an intra-cluster protocol using intra-cluster packets, the interconnection controller of each cluster interconnected by point-to-point inter-cluster links with the interconnection controller of other clusters, the computer-implemented method comprising: forming an inter-cluster packet by encapsulating an intra-cluster packet; encoding a sequence identifier in the inter-cluster packet; calculating first cyclic redundancy code check data based only upon the inter-cluster packet; encoding the first cyclic redundancy code check data in the inter-cluster packet; and transmitting the inter-cluster packet from a first cluster to a second cluster on a point-to-point inter-cluster link.