That is a significant drop in stack height. The drop from a 58 cm Domane to a 56 cm bike in the 2020 range is only 20 mm. How you have the front end of your bike setup currently also effects things as well. If you have your stem slammed currently, you may just be able to keep some spacers under the stem of the new bike to achieve the same bar height. This is all of course assuming you want to keep your position relatively similar, if you want to lower the front end then this might be fine.
I would think any shop worth doing business with would let you ride the bike and make some adjustments to stem/bar height to make sure you were comfortable before you purchase the bike, might be worth riding to see for yourself.