A processing system having a multilevel cache hierarchy employs techniques for repurposing dead cache blocks so as to use otherwise wasted space in a cache hierarchy employing a write-back scheme. For a cache line containing invalid data with a valid tag, the valid tag is maintained for cache coherence purposes or otherwise, resulting in a valid tag for a dead cache block. A cache controller repurposes the dead cache block by storing any of a variety of new data at the dead cache block, while storing the new tag in a tag entry of a dead block tag way with an identifier indicating the location of the new data.