Would be really useful if the GP Inspectors were to answer this!

I would think that it is best if you ask yourself "why do the inspectors want this information?" It is probably so that they can prepare for their inspection in which case they need to know everything as they are bound to come across all the systems whilst inspecting. It would be good to tell the inspectors that there are some systems which are not operated from the sponsor office that they will be inspecting, so that they can prepare. Remember that the inspectors may inspect the CROs you are using either as part of this inspection or as another CRO inspection.
As the sponsor (Virtual or not) will have oversight of the entire development programme of clinical trials, they will be familiar with all the computer systems being used even if they do not operate them themselves. There may be some systems (such as Serious Breaches; deviation escalation; USMs; SUSARs; etc that the Sponsor will have ands on but others which they only have general oversight of. You could ask your lead inspector what they want. I suspect they may want a list of all systems and perhaps a listing of the subgroup of those which the sponsor operates or receives frequent updates from. The MHRA GCP Guide (2012) has got stuff on Sponsor oversight.