1. A data processing system comprising a first device and a second device interconnected with a point-to-point link and operable to transmit data to each other via the point-to-point link, the first device being operable to provide data credits to the second device which facilitate transmission of the data to the first device via the point-to-point link in a plurality of virtual channels, first ones of the data credits being derived from a plurality of shared data credits each of which is operable to facilitate transmission of the data in any of the virtual channels, second ones of the data credits comprising a plurality of dedicated data credits each of which is operable to facilitate transmission of the data in a corresponding one of the virtual channels.