Rotate CubeMap Matrix

I need to rotate a cube-map about the-Y axis 180° (x+,y+,z+)->(x-,y+,z-), but I don't know how.

I believe I somehow need to manipulate the cube-map matrix from a script, by setting a matrix property, but my understanding ends there.

This is what I have help me fill in the blanks please:

Code (csharp):

1. function MatrixRotate()
2. {
3.    
4.     while(true)
5.     {
6.     yield WaitForSeconds(5.0F);
7.     Debug.Log("Flip"); 
8.     rotateMatrix=material.GetMatrix(____?____).inverse;
9.     material.SetMatrix("_RotateMatrix", rotateMatrix);
10.    
11.     yield WaitForSeconds(5.0F);
12.  
13.     }
14.    
15. }

Code (csharp):

1. Pass
2.     {    
3.         SetTexture[_MainTex] { matrix [_RotateMatrix] }
4.        
5.     }
6.  

 

Your post did really help me. and I can help you in return to fill the blank spaces:
I made a small tutorial on rotating textures:
http://themaxscriptguy.wordpress.com/2014/11/20/rotating-cubemap-in-unity/https://github.com/theMaxscriptGuy/Unity_Dev/tree/master/CubeMap_Rotation