Setting GA on my website and Unbounce pages


I want to track my unbounce page in Google Analytics. GA is already set up on my website and I have been using it for a while. I successfully added the snippet to my unbounce page (following the instructions for setting up GA on multiple subdomains).

It looks like GA Help is telling me I need to add a line to the GA snippet on my website:
_gaq.push([’_setDomainName’, ‘’]);

I have a WordPress site, I added my GA tracking code via plug-in and I don’t know where to go to add this line to my site.

Is the line of code essential? What if I leave it off my website?

If I need to add it. Where should I look for instructions on adding this to my WordPress site?