Autocomplete exteder : Clear Textbox

Hello friends

I have two text box one for country and other for city,Both are bind with Autocomplete extender and both works fine.

below is my code..

<div>
    Country :
    <asp:TextBox ID="txtCountry" runat="server" onchange="$find('AutoCompleteExtender2').set_contextKey(this.value);"></asp:TextBox>
    <cc1:AutoCompleteExtender ID="txtCountry_AutoCompleteExtender1" BehaviorID="AutoCompleteExtender1"
        runat="server" TargetControlID="txtCountry" ServiceMethod="GetCountriesList"
        ServicePath="~/services/JobPortalServices.asmx" CompletionInterval="10" CompletionSetCount="20"
        UseContextKey="true" MinimumPrefixLength="1" DelimiterCharacters="; ," EnableCaching="false"
        FirstRowSelected="true" CompletionListCssClass="completionList" CompletionListHighlightedItemCssClass="itemHighlighted"
        CompletionListItemCssClass="listItem">
    </cc1:AutoCompleteExtender>
    City :
    <asp:TextBox ID="txtCity" runat="server"></asp:TextBox>
    <cc1:AutoCompleteExtender ID="txtCity_AutoCompleteExtender1" BehaviorID="AutoCompleteExtender2"
        runat="server" TargetControlID="txtCity" ServiceMethod="GetCityList" ServicePath="~/services/JobPortalServices.asmx"
        CompletionInterval="10" CompletionSetCount="20" MinimumPrefixLength="1" DelimiterCharacters="; ,"
        FirstRowSelected="true" CompletionListCssClass="completionList" CompletionListHighlightedItemCssClass="itemHighlighted"
        CompletionListItemCssClass="listItem" UseContextKey="true">
    </cc1:AutoCompleteExtender>
</div>

i want to clear city textbox on change of country text box..