If you make your own chicken broth, you can make it carb-free. If you
use canned broth, most of them have 1 carb per 8 oz (check the label
to make sure). So it depends on how much you use. I have a tendency
to round up the number in cases like this in order to account for any
carbs the food might absorb. For example, if food X has 3.3 net carbs
per serving and I cook it in a broth, I'll count food x as 4 net
carbs.
Marinades are a different story because the meat will absorb some of
the marinade. Again, I count those carbs. So if the marinade has 8
net carbs, I count the meat I marinade in it as at least 4 net carbs.
It might be an overestimation but when it comes to counting your
carbs, it's better to overestimate than it is to underestimate.