This article is bee extracted from the URL:
http://www.inetdaemon.com/tutorials/internet/dns/servers/caching.shtml
of which many thanks for posting the article.
I extracted what I needed and posted it again here mostly for me as a reminder.

HowTo: Flush nscd dns cache

Nscd caches libc-issued requests to the Name Service. If retrieving NSS data is fairly expensive, nscd is able to speed up consecutive access to the same data dramatically and increase overall system performance. Just restart nscd:
$ sudo /etc/init.d/nscd restartOR
# service nscd restartOR
# service nscd reload
This daemon provides a cache for the most common name service requests. The default configuration file, /etc/nscd.conf, determines the behavior of the cache daemon.

Flush dnsmasq dns cache

dnsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server. This software is also installed many cheap routers to cache dns queries. Just restart the dnsmasq service to flush out dns cache:
$ sudo /etc/init.d/dnsmasq restartOR
# service dnsmasq restart
Flush caching BIND server dns cache

A caching BIND server obtains information from another server (a Zone Master) in response to a host query and then saves (caches) the data locally. All you have to do is restart bind to clear its cache:
# /etc/init.d/named restart
You can also use rndc command as follows flush out all cache:
# rndc restartOR
# 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. In this example flush all records releated to cyberciti.biz domain:
# rndc flushname cyberciti.biz
It is also possible to flush out BIND views. For example, lan and wan views can be flushed using the following command:
# rndc flush lan
# rndc flush wan
A note about Mac OS X Unix users

Type the following command as root user:
# dscacheutil -flushcacheOR
$ sudo dscacheutil -flushcache
If you are using OS X 10.5 or earlier try the following command:
lookupd -flushcache