Calculating Annual Mean NDVI for set of features using Google Earth Engine

I’m trying to calculate the annual mean NDVI for a set of polygons that are stored in a table in GEE. I want the annual mean for a series of years to be added to the table as new fields. I have the code to use the MODIS dataset to extract by day but I can’t figure out how to get the annual mean. Essentially, this output works, I just need to the annual mean instead of daily value.

var modisNDVI = ee.ImageCollection("MODIS/MCD43A4_006_NDVI").filterDate('2015-01-01', '2015-01-09');

// create dummy image.
 var stacked_image = ee.Image();

// create function to combine all images into one image as bands.
 var combine = function(img, stack){
  stack = ee.Image(stack);
  return stack.addBands(img.select([0], [img.get('system:index')]));
};

var rename_band = function(img){
  return img.select([0], [img.id()]);
};

// stack all the images into a single image.
stacked_image = modisNDVI.map(rename_band).toBands(); //iterate(combine, stacked_image);

// determine scale to perform reduceRegions.
var scale = modisNDVI.first().projection().nominalScale();
    var ndviMean = ee.ImageCollection(years).map(function(img){
      var rR = img.reduceRegions({collection: regions,
                                reducer: ee.Reducer.mean(),
                                scale: 500,
                                tileScale: 4})
      return rR.map(function(feat){
        return feat.set('year', img.get('year'))
      })
}).flatten()

Export.table.toDrive(ndviMean,"NDVI","NDVI","NDVI_zones");