component.set("v.attribute1","v.dummyAttributetoReset");

<aura:attribute name="attribute1" type="l1.LightningObject__c" default="{ 'sobjectType': 'l1__LightningObject__c',
'Name': '',
'l1__Date__c': '',
'l1__Description__c': '',
'l1__Country__c': ''
}"/>

({
    myTask : function(component, problem) {
        var action = component.get("c.saveTask");
        action.setParams({
            "task": thisTask
        });
        action.setCallback(this, function(a){
            if(a.getState() === "SUCCESS"){
                 component.set("v.problems", null);
                component.set("v.Task",
                {'sobjectType': 'obj_c',
                     'Name': '',
                     'obj__Count__c': 0,
                     'obj_String1_c': '',
                     'obj_String2__c': ''
                });

                var rSavedEvent = $A.get("e.obj:recordSaved");
                rSavedEvent.fire();
            }else{
              // Failure
            }
        });
        $A.enqueueAction(action);
    },
})

<aura:application>
    <aura:attribute name="account" type="Account"
        default="{ 'sobjectType': 'Account','Name': 'default name', 'AccountNumber': 'default account number' }"/>

    Account Name: <ui:inputText value="{!v.account.Name}"/><br/>
    Account Number: <ui:inputText value="{!v.account.AccountNumber}"/><br/>

    <ui:button label="Reset" press="{!c.clearFields}"/>
</aura:application>

({
    clearFields : function(component, event, helper) {
        component.set("v.account", {
            "sobjectType": "Account",
            "Name": "cleared Account.Name",
            "AccountNumber": "cleared Account.AccountNumber"
            }
        );
    }
})