Stopping domain and content crossover

I have several domains served by (pointing at) a single web site. I would like to run a blog for two of the domains. (One of them already has a blog – http://www.clapham-locksmiths.co.uk/blog)

I (think I) understand how to run two blogs, using the mysql prefix, etc.

However, I’d like to stop the “wrong” blog being served. Let’s say I install the second domain’s blog in “www.other.co.uk/blog_another”. Is there a recommended way to make unsuccessful the URI “http://www.other.co.uk/blog”, i.e. somebody (or google) combining the domain name of one blog with the content of the other blog?

I could add some php HTTP_HOST checking code (to index.php?) but I wondered if anyone else has to do this and if there’s a recognized way.