Is it possible for you to use the input field without an id or name attribute? Without that, the browser doesn't really have any way to associate a history with that element.
In my real quick testing on Firefox, this seemed to do the trick:
<form>
<!-- these will remember input -->
With id: <input id="myInputId" list="myList" /><br />
With name: <input name="myInputName" list="myList" /><br />
<!-- these will NOT remember input -->
No id, name, class: <input list="myList" /><br />
With class: <input class="myInputClass" list="myList" />
<datalist id="myList">
<option value="Option 1"></option>
<option value="Option 2"></option>
</datalist>
<br />
<input type="submit" />
</form>
In the code above, the inputs with an id or name would remember past values, but the input without anything and the input with just a class would not remember anything.
Unfortunately, this does make using the input slightly more difficult if you need it to have a name or id. In that case, I'd try having an id'ed input which is also display: none'ed and then use some JavaScript to keep it in sync with an input that won't remember past values.
datalist. Checked under Firefox 63.0.3 and Chromium 70.0.3538.110. Everything works as expected withautocomplete="off"