I2C - Pull-ups - Two Arduinos

For communication between two Arduinos (one being Master and the other as Slave):

a) Is it necessary that both Arduinos should share the same VCC?
b) If both Arduinos have separate VCC, to which VCC the pull-up resistors along SDA and SCL should be connected to?

a) - NO. Arduinos must share their GND
b) - It does not matter from which Arduino are pullup resistors connected, because Arduinos will have SHARED GND.

You should look to some electronics basics to understand how current flow in circuit.

Thanks, both of you for your inputs.