Top purchase: NZ herding dog (9)

I believe the answer is:

schnauzer

I'm a little stuck... Click here to teach me more about this clue!

'dog' is the definition.
(schnauzer is a kind of dog)

I cannot understand how the remainder of the clue works.

(Another definition for schnauzer that I've seen is " foreign dog".)

I've seen this clue in the Sydney Morning Herald.

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