slave to slave zone transfer

[Quadri, Jay]

sorry, not trying to confuse anybody.  My question is this:
say NS cisko.com has A & NS records for uk.cisko.com, & usa.cisko.com.
cisko.com defines usa.cisko.com & uk.cisko.com has its slave in the
named.conf
usa.cisko.com & uk.cisko.com defines cisko.com as its slave in the
named.conf
Each subdomain has cisko.com in it named.root (hint) file.  These are
Intranet DNS'es 
I noticed that cisko.com propagates to uk.cisko.com & usa.  
why do both subdomain not propagate to each other.  I would have thought
this will happen since cisko.com is slave to both subdomain. 
cisko.com, uk.cisko.com & usa.cisko.com are all located on differ sites.
I don't want to define uk.cisko as slave on usa. nor do I want to define usa
as slave on uk.  

Hope this is clearer.