In the open office environment I used to work in I got quite good at ignoring coworkers discussions about stuff they were working on. But as they crammed more and more people into the building, the probability of being within earshot of multiple discussions at once went up. I could sit in my chair getting angry when there was only two. When it got to three concurrent discussions I found I had to leave the vicinity. Some people could ignore it all. Impressive.

Ideally, if it's something important to you, your coworkers should get your attention, or at least communicate the results of their discussion to you.

But I realize that this is supposing two idealized coworkers in a perfect vacuum.

Right, it's whether or not I can put the conversation into a context. If not, it's just noise. If I can organize it or think about how accurate the information is, you have my un-un-divided attention.