1. A method comprising: receiving a prefetch command in an input/output (I/O) memory management unit (IOMMU), wherein the prefetch command specifies a virtual address, wherein the prefetch command is transmitted by a processor that has a processor MMU that is separate from the IOMMU, wherein the processor MMU is configured to translate virtual addresses from the processor to physical addresses; reading translation data from one or more I/O translation tables in system memory of a system that includes the IOMMU, wherein the reading is responsive to the virtual address and to an I/O translation mechanism implemented by the IOMMU to translate virtual addresses in direct memory access (DMA) requests transmitted by one or more I/O devices; and storing data in one or more caches of the IOMMU responsive to the reading.