On the Web, if a selection is made in a multi-value list field, I have found that many of our users do not know how to completely deselect the options chosen.
I usually place this code next to the field on my Notes form. Using the standard view icons for Domino, a small red 'x' appears to the right of the field. Clicking on this graphic will trigger the onClick and set the field to "".
To reuse this just replace "FieldName" in document.forms.FieldName.value with the name of your field. You could also use this for fields other than multi-value fields.
<a href="" onClick="document.forms.FieldName.value=''; return false;"><img src="/icons/vwicn081.gif" border=0></a>