It may be worth asking the OP... Can you pls explain your understanding / expectations of DMA.
DMA will never access an Arduino's on-chip RAM...
If a particular processor family supports DMA, it is either designed for that role, or has on on-chip DMA controller peripheral... just like a UART or RTC on chip.
An application host CPU simply sets up the memory transfer in the 'separate' DMA controller's logic, so it can be executed outside the view/control of the host CPU. After setup, and saying 'go', the host CPU never knows about the transfer until it is complete, or an exception is raised.