A method for scheduling tasks to be processed by one of a plurality of non-coherent processing devices, at least two of the devices being heterogeneous devices and at least some of said tasks being targeted to a specific one of the processing devices. The devices process data that is stored in local storage and in a memory accessible by at least some of the devices. The method includes the steps of: for each of a plurality of non-dependent tasks to be processed by the device, determining consistency operations required to be performed prior to processing the non-dependent task; performing the consistency operations for one of the non-dependent tasks and on completion issuing the task to the device for processing; performing consistency operations for a further non-dependent task such that, on completion of the consistency operations, the device can process the further task.