If this is so the probability of a clean sheet for either team is determined by the mean number of goals to be expected by the other team when playing the team in question given the current state of form.
A simple model might be (assuming I have understood your notation):
Sore(A)=OAGSC/2 + (AGS(A)-OAGSC/2) - (AGC(B)-OAGSC/2)
Sore(B)=OAGSC/2 + (AGS(B)-OAGSC/2) - (AGC(A)-OAGSC/2)
But you should also include some correction for home team advantage (I beleive there was a paper on this recently on ArXiv.org but I don't have a link for that).