A method of operating a system comprises multiple processor tiles divided into a plurality of domains, wherein within each domain the tiles are connected to one another via a respective instance of atime-deterministic interconnect and between domains the tiles are connected to one another via a non-time-deterministic interconnect. The method comprises: performing a compute stage, then performinga respective internal barrier synchronization within each domain, then performing an internal exchange phase within each domain, then performing an external barrier synchronization to synchronize between different domains, then performing an external exchange phase between the domains.