Connecting Atmel ICE to MKR board - multiple grounds

I’m making a cable to connect my Atmel ICE to my MKR GSM1400. The Atmel ICE has a 10 pin IDC connecter; The pin mapping is below as per the datasheet:

Name AVR port pin SAM port pin Description
SWDC 1 4 Serial Wire Debug Clock. LK
SWDIO 5 2 Serial Wire Debug Data Input/Output.
SWO 3 6 Serial Wire Output (optional- not implemented on all devices).
nSRST 6 10 Reset.
VTG 4 1 Target voltage reference.
GND 2, 10 3, 5, 9 Ground.

The table doesn’t specify whether to connect all three grounds for a SAM SWD target, whereas it explicitly specifies to do so for a SAM JTAG target.

Why would there be multiple grounds and does an SWD target require all of them or just one?

Why would there be multiple grounds and does an SWD target require all of them or just one?

There are not multiple grounds, there is 1 ground* with 2 or 3 connections to it. As long as a ground on one device is connected to a ground on the other it should be OK.

*If you doubt this go outside and look around, how many grounds do you see?