primefaces remotecommand partial process - primefaces

Question

I am working on webflow 2.3.1, primefaces 3.4.2 project.
As you see, i tried to update selectOneMenu according to parent city as shown at example from primefaces showcase. However i used p:remoteCommand to call webflow action.
At remoteCommand , if i set process="#this, subSelectOneMenu", action did not call . But if i did not set "process",it called action but it also give error for captcha which is empty.
How can i use remoteCommand to call action partially?
<h:form id="signUpUserInfo">
<p:panelGrid id="grid" columns="2">
<p:selectOneMenu id="citySelectOneMenu" value="#{userBean.address.cityId}" label="#{label.address_city}" onchange="selectionChanged()">
<f:selectItem itemValue="" itemLabel="" />
<f:selectItems value="#{flowScope.cityList}" />
</p:selectOneMenu >
<p:selectOneMenu id="subSelectOneMenu"
value="#{userBean.address.subId}" label="#{label.address_sub}">
<f:selectItem itemValue="" itemLabel="" />
<f:selectItems value="#{flowScope.subList}" />
</p:selectOneMenu>
<p:captcha id="captcha" label="Captcha" language="en" theme="white" required="true" secure="true" />
<f:facet name="footer">
<p:commandButton id="save" value="#{label.save_button}" ajax="false"
action="signUpStandartMember" update="signUpUserInfo" />
</f:facet>
</p:panelGrid>
<p:remoteCommand id="selectionChanged" name="selectionChanged" action="cityChangedAction" update="subSelectOneMenu" process="#this, subSelectOneMenu" />
</h:form>