If you are wanting to choose 1 of the 2 reguins, this should work. Assuming your lists are in columns A:C, something like this array formula will work:
=NETWORKDAYS(StartDay,EndDay,IF(C2:C20="Chennai",A2:A20,0))
Make sure that you confirm array formulas using Ctrl+Shift+Enter, not just Enter.
If you did intend to use both region's holidays, it shouldn't make any difference. You can just include all the holidays in the formula, even if there are duplicates.