Thanks for further information. Since they were cousins than I would think they were from basically same area of Poland.
There are two Zablocie close to Krakow. http://mapa.szukacz.pl
but the Zablocie closes to Krakow is in Malopolskie woj. powiat Wielicki, gmina Biskupice.
In Malopolskie phone book a surname HERZYK, KUSAK, and HAPEK. www.ksiazka-telefoniczna.com
The word Potok is Slavic.