All you have to do is restart bind to clear its cache:
root# /etc/init.d/named restart
You can also use rndc command as follows flush out all cache:
root# rndc restart
or
root# rndc exec
BIND v9.3.0 and above will support flushing all of the records attached to a particular domain name with rndc flushname command.
root# rndc flushname domain.name.com
It is also possible to flush out BIND views. For example, lan and wan views can be flushed using the following command:
root# rndc flush lan
root# rndc flush wan