A processor can operate in three different modes. In an active mode, a first voltage is provided to the processor, where the first voltage is sufficient to allow the processor to execute instructions. In a low-power mode, a retention voltage is provided to the processor. The processor consumes less power in the retention mode than in the active mode. In addition, the processor can operate in a third mode, where a voltage is provided to the processor sufficient to allow the processor to process cache messages, such as coherency messages, but not execute other normal operations or perform normal operations at a very low speed relative to their performance in the active mode.