After installing Urchin, I got the following error when trying to update _domaindb.

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1ERROR: (7066-211-368) Domain DB update failed DETAIL: (6) Couldn't resolve host 'download.urchin.com'

Now the DNS was configured properly and download.urchin.com was pinging normally.

Turns out that urchin needs the nscd service enabled.

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1#yum install nscd
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.