Limit plugin to blog admin only -> check priviledges

I've been playing around with some plugins and have created my custom ones based on those. Though, I ran to a major bug while beta testing those plugins:

It seems like when blog address is something.domain.com and plugin editor settings page is

something.domain.com/wp-admin/admin.php?page=plugin.php

blog owner of something.domain.com can also access

somethingelse.domain.com/wp-admin/admin.php?page=plugin.php and change settings.

I'd appreciate if you could help me with this and tell how to check if user have priviledges to modify setting of other blog.

I know it's quite easy thing to do (lol, for someone who CAN DO IT), but I just can't figure it out... I just don't wan't to create SQL statements when I know it's already build in MU.

btw, these plugins are in plugins, not mu-plugins folder if it makes any difference.