A roaming local cat weed on my porch and front door mat. I had to throw the mat out but after washing the porch with a solution of white vinegar we haven't had any more problems. Also i bought a new doormat which i guess doesn't smell of cats (yet!)
The only thing I've found that gets rid of cat urine smell (and I had tried everything - bio washing liquid, white vinegar, bicarb etc etc) was that MN favourite - Zoflora. The citrus one is particular good. But really it's a revelation.