Multiple Tag Groups/Sets for separate channels
Sounds like two different relation fields - linked with two different categories - would fit much better for your needs. When you create Tags/Taggroups everybody can insert everything so you can't forbid equal tags unless you hook into an event with php to prevent the saving process. When you create two different tag fields their autocomplete sources will be different but you can insert whatever you want.

So what you want to do is: create 2 different categories: The first News the second Reviews and add your keywords there. Then you create two relation fields, one linked with News, the other one linked with Reviews. Then you add those to your field layout