Google Now will do some coreferences, but Siri is almost modal. You can talk to it like an assistant instead of trying to formulate everything as a search query. I had a Nexus 5 almost a year before getting my 6+, and I was always jealous of how much more practically useful Siri was on my wife's iPhone 5.
Me: "Siri, find me a target."
<finds several targets>
Me: "Directions."
Siri: "Which target?"
Me: "Third one."
<gives directions to third one in list>
Also:
Me: "Siri, find me restaurants."
<lists restaurants>
Me: "Review for Blue Duck Tavern"
<lists review>
Me: "Other restaurants"
<lists restaurants>
Me: "Reservation for Founding Farmers."
Google Now will do some coreferences, but Siri is almost modal. You can talk to it like an assistant instead of trying to formulate everything as a search query. I had a Nexus 5 almost a year before getting my 6+, and I was always jealous of how much more practically useful Siri was on my wife's iPhone 5.