How do I reflect an object over an axis?

[EmNudge]

I have a basic symmetrical map and I'd like to flip a complex bunch of brushes over an axis.
I can individually match up the vertex points so that they are a reflection of their sister brushes, but that'd take a very long time.

Is there any quick way to do this?

 

[theatreTECHIE]

Control-L or Control-I

 

[Phil25]

I usually open the Transformation menu with Ctrl+M and scale an axis to -1.