As far as I've been able to find (please correct me if I am wrong!), there is no current technology that would permit an EVA suit that is being worn to be sterilized without risk of damage to the suit or the astronaut. For example, infrared could be used, but would be at risk of damaging the suit after repeated exposures, and could damage the astronaut if the helmet did not block the IR sufficiently. This would be for situations such as when the astronaut is preparing to go out onto a planet surface, so doing a wipe-down in a clean room is not a practical solution.
Is there any process that is currently being developed, that is known about but not currently possible, or that is likely to be discovered, which could allow the exterior of an EVA suit to be sterilized immediately prior to an EVA?