DNS caches that support partitioning ?

["John Levine" <johnl () iecc com>]

Are there DNS caches that allow you to partition the cache for
subtrees of DNS names?  That is, you can say that all entries from
say, in-addr.arpa, are limited to 20% of the cache.

The application I have in mind is to see if it helps to keep DNSBL
traffic, which caches poorly, from pushing other stuff out of the
cache, but there are doubtless others.

R's,
John