Nissan X-Trail 2011: Injection flush

We have a 2011 Nissan X-Trail and, at the recent 70,000km service at a Nissan dealer, an injection flush for $223 was recommended. We have never heard of this and the handbook doesn't recommend it. I asked about the purpose and benefits of an injection flush, but the dealer's rep's answer was a bit vague. What's your view on injection flush?