disjoin a subdomain from and still keep the subdomain intact???

I just inherited a small segment of a larger network configured as so:

The larger network has a domain largernetwork.com
Another domain was created called smallnetwork.com which trusts
largernetwork.com
Finally another child domain was created smaller.smallnetwork.com.

The latter 2 domains (smallnetwork.com and smaller.smallnetwork.com) consist
of 4 servers. Two domain controllers per domain. Smallnetwork.com consists
of the two domain controllers and thats it for that whole domain. Anyway the
domain smaller.smallnetwork.com network includes some important servers
(there are more than two domain controllers like smallnetwork.com). Why this
was set up this way I have no idea..

What I would like to do is get smaller.smallnetwork.com out from underneath
small.network.com. Four domain controllers for this network is overkill. How
can I do this without creating an inoperable smaller.smallnetwork.com
domain? I hope I made my scenario clear....

Thanks in advance