Tipster Lloyd Beachy shares a trick in AutoCAD to get rid of unwanted layers that are hiding in your blocks.
"When working with blocks that have been copied from one drawing to another, I will invariably come across a block that has pulled in layers that I didn’t want to have included.
"If you know which block is the offending block, you can edit the block definition, change the objects to layer 0, then purge out the layer (assuming no other blocks use that layer). A much easier way to do this is with the Layers Property Manager. Simply right-click on the unwanted layer and select Merge selected layer(s) to… You will be asked to specify the target layer you want the objects moved to. This will cover every block in the drawing and purge out the layer with one simple step."
Notes from Cadalyst tip reviewer Brian Benton: Blocks often have hidden "gems" that we don’t really want: layers, text styles, dim styles, etc. This tip provides an easy way to get rid of those unwanted layers. It even works for layers that aren’t in a block but you want them gone anyway. The Merge layers option will move all of the objects on a specific layer to another layer, then delete the offending layer. No data is lost — just the layer. This is a handy tool to use when you get a file that has a layering system you just don’t want to use. You can also use this trick to migrate objects to a specific layer. Maybe your company’s layer practices or standards have changed. Or perhaps you have files from three different agencies and they each used a different layer name for the same thing.