Interesting, the system description for us drivers reads:
The recirculation fan system reduces the air conditioning system pack load and the engine bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to the forward cargo bay where it is filtered and recirculated to the mix manifold. The fan is driven by an AC motor. The fan operates with the recirc fan switch in AUTO except with both packs on and one or both in HIGH.
That seems to indicate that the forward cargo hold is heated and ventilated by the used air from the electrical equipment compartment and used cabin air.