Cache storage may be partitioned in a manner that dedicates a first portion (e.g. 81) of the cache to lockstep mode execution, while providing a second (or remaining) portion (e.g. 82) for non-lockstep execution mode(s). For example, in embodiments that employ cache storage organized as a set associative cache, partition may be achieved by reserving a subset of the ways in the cache for use when operating in lockstep mode. Some or all of the remaining ways are available for use when operating in non-lockstep execution mode(s). In some embodiments, a subset of the cache sets, rather than cache ways, may be reserved in a like manner, though for concreteness, much of the description that follows emphasizes way-partitioned embodiments.