multi-db: Joins between global tables and blog tables

I did some searching around on the forum and didn't find a thread that speaks to this issue (but I might have missed it, so apologies in advance).

I am assuming that doing a join between a global table and a blog table is not kosher. Correct?

Or, is it my lucky day, and the multi-db class does some magic to make this possible?

Here's a simple example of the type of thing I know exists in some of the code...

SELECT * FROM $table_blog_posts, $table_blogs
WHERE $table_blogs.public = 1 AND $table_blogs.deleted = 0 AND $table_blogs.spam = 0;

Now clearly this code can be rewritten to confirm the publicness and the non-spamness and non-deletedness of the blog before it attempts to do the select... but I see this sort of thing in plugins around... Hell, I admit, I wrote some code that does this.

So, if I am correct that this code needs to be rewritten... then... does anyone have any strategies on hunting down this kind of code.

Thanks in advance.