How to query the "incoming" serial of a zone while inline signing

[Klaus Darilion]

Hi!

I use Bind for inline signing between a hidden master and the public 
slaves. AFAIS Bind maintains 2 serials: one for the incoming unsigned 
zone (eg. used to match incoming NOTIFYs) and one for the outgoing 
signed zone.

I want to monitor if my name servers are all up2date by monitoring and 
comparing the serial. This works to compare the serial of the public 
slave with the outgoing serial of Bind. But if I want to know if Bind is 
in sync with the hidden master, I somehow have to find out the 
"incoming" serial of Bind.

Are there any tools/ways to query Bind for the incoming serial?

Thanks
Klaus