Depending on what it is, a little warm/hot soapy water should do. When we had our double-entry exterior doors installed, clear caulking was used where the threshold meets the outside step. EVERYTHING tends to stick to it. And all I use is what I said.
If that doesn't work, try some Windex or something. Test it on an inconspicious area first. It may do a better job than you expect! If that's the case, you may create more work for you. Maybe you need to dilute your mix or use less 'elbow grease'.