Memories are currently a real bottleneck to design high speed and energy-efficient systems-on-chip. A significant increase of the performance gap between processors and memories is observed. On the other hand, an important proportion of total power is spent on memory systems due to the increasing trend of embedding volatile memory into systems-on-chip. For these reasons, STT-MRAM (Spin-Transfer Torque Magnetic Random Access Memory) is seen as a promising alternative solution to traditional SRAM (Static Random Access Memory) thanks to its negligible leakage current, high density, and non-volatility. Nevertheless, the strategy of the same footprint replacement is constrained by the high write energy/latency of STT-MRAM. This paper performs a fine-grained evaluation of the cache organization to propose a hybrid cache memory architecture including both SRAM and STT-MRAM technologies.