sorry for the late reply.
You can bring the canvas to Hermès, they will clean it for you, at least in Europe they provide that service.
The earlier Herbags were ease to detach (and therefor to clean) but the Herbag zip is quite a hard thing to detach if not impossible (didn't try it yet).
You can detach at least part of it. One one side the round piece screws in. You unscrew it, then there is a detachable metal piece inside. You can then just slide the bar out the other side. You can do this to remove the long strap. You also have to dismantle the metal closure to get the sangles off. I haven't figured that part out yet.
Imho the B I have is easier to clean as the Herbag, this is why I use the Herbag less often.