Invert/Reflect mesh...?

Hi all,
I need to invert a mesh I have in order to produce a mirror copy, i.e. to mirror in the x plane. The mesh is very large (deriving from a laser scan)… I know there is an answer somewhere but just cant get my head around it.
Thanks for any help,

scale the model to -1 along the x-axis

Perfect, thanks Morio! I knew it was there somewhere…