After installing Urchin, I got the following error when trying to update _domaindb.
Now the DNS was configured properly and download.urchin.com was pinging normally.
Turns out that urchin needs the nscd service enabled.
2#chkconfig nscd on
3#service nscd start
4#ln -s /var/run/nscd/socket /var/run/.nscd_socket
After doing this, the update should work fine.