Many new nonvolatile memory (NVM) technologies have been heavily studied to replace the power-hungry SRAM/DRAM-based memory hierarchy in today's computers. Among various emerging NVM technologies, Spin-Transfer Torque RAM (STT-RAM) has many benefits, such as fast read latency, low leakage power, and high density, making it a promising candidate for last-level caches (LLCs). 1 However, STT-RAM write operation is expensive. In particular, a long STT-RAM cache write operation might obstruct other cache accesses and result in severe performance degradation. Consequently, how to mitigate STT-RAM write overhead is critical to the success of STT-RAM adoption. In this article, we propose an obstruction-aware cache management policy called OAP. OAP monitors cache traffic, detects LLC-obstructive processes, and differentiates the cache accesses from different processes. Our experiment on a four-core architecture with an 8MB STT-RAM L3 cache shows a 14% performance improvement and 64% energy reduction.