How to delete layers

Hello!

I've written little proggy to put all the objects (event within blocks
and their attributes) on the same layer (usally 0).
But after I do that, I cannot delete the remaining layers, although
they are empty (no objects are on them). I now that they are empty for
sure, because if I explode all the blocks, purge all that I can and
then select all the objects, they are on the same layer. Even with
filter command I can not get anything selected on other layers, but
somehow autoacad thinks that they still contain objects.

How can I purge the remaining layers?

Any help is greatly appriciated, Charlie!