for /f %%D in ('dir/s/b/ad ^| find/i "obj" ') do rd/s/q %%D

http://www.experts-exchange.com/Programming/Languages/Scripting/Shell/Batch/Q_23740037.html

Although file wildcards can be used to delete files recursively, it's not as simple for directories. This example will recursively remove 'obj' directories.

Remove directories recursively - Similar to rd /r obj

DOS Batch