Mostly Metropolitan Region as per Railways start from Karjat/Kasara in CR, Dahanu in WR & Probably(Not Sure) Panvel in Harbour Line.....Actual Mumbai Suburbs/City Limits start from Mulund in CR, Dahisar in WR & Mankhurd in Harbour Lines.... It's only after Thane District in CR/WR & Navi Mumbai City in Harbour Line ends, Mumbai Limits begin.
So technically, Mumbai does not have any Passing Trains. It has only Originating/Terminating Trains as all trains bypass from Diva(Thane District), Vasai (Palghar District) & Panvel(Raigad District) itself without touching Mumbai. But still some passengers call the outskirts also as Mumbai only as it belongs to Metropolitan Region as per Railway Boundaries.